[netstack] Move SO_REUSEPORT and SO_REUSEADDR option to SocketOptions.

This changes also introduces:
- `SocketOptionsHandler` interface which can be implemented by endpoints to
  handle endpoint specific behavior on SetSockOpt. This is analogous to what
  Linux does.
- `DefaultSocketOptionsHandler` which is a default implementation of the above.
  This is embedded in all endpoints so that we don't have to uselessly
  implement empty functions. Endpoints with specific behavior can override the
  embedded method by manually defining its own implementation.

PiperOrigin-RevId: 343158301

1 files changed, 61 insertions, 0 deletions

diff --git a/pkg/tcpip/socketops.go b/pkg/tcpip/socketops.go
index cc3d59d9d..99c3e9c45 100644
--- a/pkg/tcpip/socketops.go
+++ b/pkg/tcpip/socketops.go
@@ -18,11 +18,36 @@ import (
 	"sync/atomic"
 )
 
+// SocketOptionsHandler holds methods that help define endpoint specific
+// behavior for socket options. These must be implemented by endpoints to get
+// notified when socket level options are set.
+type SocketOptionsHandler interface {
+	// OnReuseAddressSet is invoked when SO_REUSEADDR is set for an endpoint.
+	OnReuseAddressSet(v bool)
+
+	// OnReusePortSet is invoked when SO_REUSEPORT is set for an endpoint.
+	OnReusePortSet(v bool)
+}
+
+// DefaultSocketOptionsHandler is an embeddable type that implements no-op
+// implementations for SocketOptionsHandler methods.
+type DefaultSocketOptionsHandler struct{}
+
+var _ SocketOptionsHandler = (*DefaultSocketOptionsHandler)(nil)
+
+// OnReuseAddressSet implements SocketOptionsHandler.OnReuseAddressSet.
+func (*DefaultSocketOptionsHandler) OnReuseAddressSet(bool) {}
+
+// OnReusePortSet implements SocketOptionsHandler.OnReusePortSet.
+func (*DefaultSocketOptionsHandler) OnReusePortSet(bool) {}
+
 // SocketOptions contains all the variables which store values for SOL_SOCKET
 // level options.
 //
 // +stateify savable
 type SocketOptions struct {
+	handler SocketOptionsHandler
+
 	// These fields are accessed and modified using atomic operations.
 
 	// broadcastEnabled determines whether datagram sockets are allowed to send
@@ -36,6 +61,20 @@ type SocketOptions struct {
 	// noChecksumEnabled determines whether UDP checksum is disabled while
 	// transmitting for this socket.
 	noChecksumEnabled uint32
+
+	// reuseAddressEnabled determines whether Bind() should allow reuse of local
+	// address.
+	reuseAddressEnabled uint32
+
+	// reusePortEnabled determines whether to permit multiple sockets to be bound
+	// to an identical socket address.
+	reusePortEnabled uint32
+}
+
+// InitHandler initializes the handler. This must be called before using the
+// socket options utility.
+func (so *SocketOptions) InitHandler(handler SocketOptionsHandler) {
+	so.handler = handler
 }
 
 func storeAtomicBool(addr *uint32, v bool) {
@@ -75,3 +114,25 @@ func (so *SocketOptions) GetNoChecksum() bool {
 func (so *SocketOptions) SetNoChecksum(v bool) {
 	storeAtomicBool(&so.noChecksumEnabled, v)
 }
+
+// GetReuseAddress gets value for SO_REUSEADDR option.
+func (so *SocketOptions) GetReuseAddress() bool {
+	return atomic.LoadUint32(&so.reuseAddressEnabled) != 0
+}
+
+// SetReuseAddress sets value for SO_REUSEADDR option.
+func (so *SocketOptions) SetReuseAddress(v bool) {
+	storeAtomicBool(&so.reuseAddressEnabled, v)
+	so.handler.OnReuseAddressSet(v)
+}
+
+// GetReusePort gets value for SO_REUSEPORT option.
+func (so *SocketOptions) GetReusePort() bool {
+	return atomic.LoadUint32(&so.reusePortEnabled) != 0
+}
+
+// SetReusePort sets value for SO_REUSEPORT option.
+func (so *SocketOptions) SetReusePort(v bool) {
+	storeAtomicBool(&so.reusePortEnabled, v)
+	so.handler.OnReusePortSet(v)
+}